Modern electronic devices provide a staggering array of functionality to users. Portable handheld electronic devices such as telephones, music players, PDA's, and game players can display information on display screens, receive instructions from a user, communicate with other devices using wired and wireless data links, take digital photographs, and process large volumes of digital data at speeds that were unthinkable even a generation ago.
Such functionality can be provided, in part, using graphical displays that act as both inputs and outputs. For example, touch screens include a display screen and detect the presence and location of manual interaction with that display screen. A user can interact with the elements shown on the display screen intuitively, in ways that resemble the ways that humans interact with the world outside of graphical displays and electronic devices.